1. Field of the Invention
The present invention relates to certain novel anti-neoplastic, anti-viral and ribonucleotide reductase catalytic activity affecting pharmaceutical compositions and methods of treatment.
2. Prior Art
Due to the critical role played by iron in the function of a variety of biological redox systems, e.g., ribonucleotide reductase, electron transport proteins, iron flavorproteins, hydroperoxidase and oxygenases, life, with the possible exception of the lactobacilli, without iron is essentially unknown.
Microorganisms are particularly sensitive in their iron requirement and many have evolved remarkable mechanisms for iron acquisition. They synthesize low molecular weight, virtually ferric ion specific chelators, i.e., siderophores which assist transport of exogenous iron into the cell where it is utilized in supporting growth [Neilands, Ann. Rev. Biochem. 50, pp. 715-731 (1981); Bergeron, Chem. Rev. (in press) (1984); Emery, Metal Ions in Biological Systems, pp. 77-121 (1973)]. Many of these chelators are relatively simple molecules consisting of catechol moieties (e.g., 2,3-dihydroxybenzoyl groups) attached to various amine backbones. All of these ligands bind iron tenaciously; e.g., parabactin, a siderophore synthesized by the plant pathogen, Paracoccus denitrificans [Tait, Biochem. 146, pp. 191-197 (1975)], forms a 1:1 metal complex with an iron formation constant in the order of 10.sup.48 moles/1.
Although certain microbes can interchangeably utilize the siderophores of other prokaryotes, this ability is not universal. It has recently been shown, for example, that parabactin cannot be utilized by large numbers of bacterial pathogens [Bergeron et al, Antimicrob. Agents and Chemo. 24., pp. 725-730 (1983)]. In fact, the siderophore exhibits potent bacteriostatic and fungistatic effects and appears to act by competing with microbes for available iron.
Weinberg [Nutrition and Cancer 4, pp. 223-233 (1983) and Physiological Reviews 64, pp. 65-96 (1984)] has provided a compelling rationale for iron-withholding as a strategy against infection and neoplasia. Porter et al [Cancer Research 42, pp. 4072-78 (1982)] has shown that N.sup.1, N.sup.8 -dihydroxybenzoylspermidine demonstrates significant cytotoxicity to L1210 cells (50% growth-inhibitory dose, 10 .mu.M) and postulates that the activity is probably attributable to its iron-chelating properties. However, not all iron chelators exhibit cytotoxicity.
It is an object of the present invention to provide certain anti-neoplastic, anti-viral, anti-psoriasis, anti-malarial and ribonucleotide reductase activity affecting pharmaceutical compositions and methods of treatment wherein the active agent is one of a small class of specific iron chelators.